1. Field of the Invention
The present invention relates to a technique for connecting interconnect lines and more particularly, to a technique for connecting a pair of interconnect lines in a semiconductor device stacked in a direction of a thickness of the semiconductor device, for example.
2. Description of the Background Art
In a semiconductor integrated circuit undergoing development in scaledown, attention has been directed to interconnection delay as a factor in inhibiting increase in operating speed of a device. The delay in semiconductor integrated circuit is the sum of the delay in transistor as a semiconductor element and the delay in interconnection for connecting transistors. When it is required to reduce dimensions of each type of element for constituting the semiconductor device for realizing scaledown, the delay in transistor is reduced according to a scaling law. In contrast, the interconnection delay determined in proportion to the product of interconnection resistance and interconnection capacitance is increased. In view of this, it follows that the reduction in interconnection resistance brings reduction in interconnection delay, offering enhanced speed of the semiconductor device.
Instead of aluminum-based material conventionally employed, it has been suggested to employ copper (Cu) as a material for interconnection having a lower resistivity. An interconnect line made of copper (hereinafter referred to as xe2x80x9ccopper interconnect linexe2x80x9d) is desirable as compared with an interconnect line made of aluminum-based material in that it has a high resistance to electromigration.
As compared with aluminum-based interconnection material, however, it is hard to perform dry etching on copper. For this reason, in order to form the copper interconnect line, a so-called xe2x80x9cDamascenexe2x80x9d technique is employed in many cases. According to this technique, a trench is provided in an insulating film. This trench is filled with metal and a redundant part of metal is removed by polishing, for example. Then the metal remains in the trench is employed as an interconnect line.
Copper is further characterized in that when it goes into silicon, a deep level is formed in a band gap of silicon. Therefore, copper included in a MOS transistor for constituting an integrated circuit will cause a serious deterioration in characteristics of the MOS transistor. In addition, copper is likely to diffuse into a silicon oxide film generally used as an insulating layer of the semiconductor device. In view of the foregoing, it is necessary to surround the copper interconnect line with a film for preventing diffusion of copper.
FIG. 13 is a sectional view illustrating the structure of a pair of copper interconnect lines provided by Damascene technique. An insulating film 101, a first insulating barrier layer 104, an interlayer insulating film 105 and a second insulating barrier layer 108 are stacked in this order. Also provided under the insulating film 101 (that is, on the side opposite to the second insulating barrier layer 108) is a semiconductor substrate (not shown) for holding a semiconductor element formed therein.
A copper interconnect line 102 is embedded in the insulating film 101 and the bottom surface and side surfaces of the first copper interconnect line 102 are covered with a first conductive barrier layer 103. A second copper interconnect line 106 is embedded in the interlayer insulating film 105 and the bottom surfaces and side surfaces of the second copper interconnect line 106 are covered with a second conductive barrier layer 107. The first copper interconnect line 102 and the second copper interconnect line 106 are positioned adjacent to each other through the second conductive barrier layer 107 and electrically connected to each other. Except this neighboring area, the first copper interconnect line 102 and the second copper interconnect line 106 are isolated from each other by the first insulating barrier layer 104 and the interlayer insulating film 105. When further copper interconnect line is provided in the interlayer insulating film 105 other than the second copper interconnect line 106, it is a matter of course that the copper interconnect other than the second copper interconnect line 106 and the second copper interconnect line 106 are to be isolated from each other by the interlayer insulating film 105.
A silicon oxide film is applicable as the insulating film 101 and the interlayer insulating film 105, for example. As the first insulating barrier layer 104 and the second insulating barrier layer 108, a silicon nitride film and a silicon carbide film are applicable, for example, for increasing strength of the insulating film 101 and the interlayer insulating film 105 and for obtaining isolation between the layers. As the first conductive barrier layer 103 and the second conductive barrier layer 107, a metallic compound having conductivity is employed in many cases for reducing interconnection resistance and establishing electrical connection between the first copper interconnect line 102 and the second copper interconnect line 106 while preventing diffusion of copper from the copper interconnect lines into the insulating film 101 and the interlayer insulating film 105.
However, the silicon oxide film to be employed as the insulating film 101 and the interlayer insulating film 105 has a thermal expansion coefficient of 1.21xc3x9710xe2x88x927/K while copper has a thermal expansion coefficient of 1.67xc3x9710xe2x88x925/K. That is, the thermal expansion coefficient of copper is considerably higher than that of the silicon oxide film. After formation of the copper interconnect lines, thermal processings are performed for forming the insulating films or in an atmosphere including hydrogen and in a temperature of about 400xc2x0 C., for example, for recovering damage to the semiconductor element not shown such as a transistor that is caused during formation of the copper interconnect lines. Further, the rise in temperature is caused by Joule heat that is generated upon energizing the semiconductor integrated circuit. It view of these, it follows that there occurs tensile stress in the copper interconnect lines.
Turning to the metallic compound to be employed as the first conductive barrier layer 103 and the second conductive barrier layer 107 having the property of preventing diffusion of copper into the outside, it generally has poor adhesion to copper. Further, the second copper interconnect line 106 has a small diameter at the region neighboring on the first copper interconnect line 102 and the tensile stress described above is likely to be concentrated especially at this region. As a result, a void may be generated in the second copper interconnect line 106 at the region of a small diameter thereof (contact hole). This void will cause failure in electrical connection between the second copper interconnect line 106 and the first copper interconnect line 102.
As a countermeasure against the foregoing, a technique of using a stacked layer including titanium having good adhesion to copper and a metallic compound sandwiched between titanium has been suggested as a structure especially of the second conductive barrier layer 107. According to the structure illustrated in FIG. 13, Japanese Patent Application Laid-Open No. 2000-183064 discloses, for example, the technique of providing a barrier layer having a three sublayer structure of Ti/TiN/Ti between the second copper interconnect line 106 and the first copper interconnect line 102.
In the structure having direct connection between titanium (Ti) and copper, however, there arises a problem in that titanium easily diffuses into the copper interconnect lines to thereby form an alloy. The alloy formed in this way has a resistivity higher than that of copper and therefore, causes rise in interconnection resistance and in interface resistance at the contact hole.
A first aspect of the present invention is directed to a structure for connecting interconnect lines, comprising: a first copper interconnect line; a second copper interconnect line including a first portion and a second portion having a diameter smaller than that of the first portion; and an interposed layer provided between the first copper interconnect line and the second portion, wherein the interposed layer includes a first metal layer made of an element having an atomic weight higher than that of copper, and the first metal layer is in contact with the second portion.
According to a second aspect of the present invention, the structure for connecting interconnect lines of the first aspect further comprises an interlayer insulating film in which the second copper interconnect line is embedded.
According to a third aspect of the present invention, in the structure for connecting interconnect lines of the first or second aspect, the interposed layer further includes a metallic compound layer provided on a side opposite to the second copper interconnect line with the first metal layer provided therebetween.
According to a fourth aspect of the present invention, in the structure for connecting interconnect lines of the third aspect, the interposed layer further includes a second metal layer having contact with the first copper interconnect line.
According to a fifth aspect of the present invention, in the structure for connecting interconnect lines of the fourth aspect, the second metal layer is made of an element having an atomic weight higher than that of copper.
According to a sixth aspect of the present invention, in the structure for connecting interconnect lines of the fifth aspect, the first metal layer and the second metal layer are made of a same metallic element, and the metallic compound layer includes the same metallic element as a main metallic element thereof.
According to a seventh aspect of the present invention, in the structure for connecting interconnect lines of the third aspect, the first metal layer has a thickness larger than that of the metallic compound layer.
According to an eighth aspect of the present invention, in the structure for connecting interconnect lines of any one of the first to seventh aspects, the thickness of the first metal layer is 1 nm or more.
An ninth aspect of the present invention is directed to a method of manufacturing a structure for connecting interconnect lines, comprising the steps of: (a) forming a first copper interconnect line; (b) forming an interposed layer on the first copper interconnect line; and (c) forming a second copper interconnect line on the interposed layer, wherein the step (b) comprises the steps of: (b-1) forming a metallic compound layer after the step (b); and (b-2) forming a first metal layer on the metallic compound layer, contact is established between the second copper interconnect line and the first metal layer in the step (c), and the first metal layer is made of a metallic element having an atomic weight higher than that of copper.
According to a tenth aspect of the present invention, in the method of manufacturing a structure for connecting interconnect lines of the ninth aspect, the step (b-1) and the step (b-2) are sequentially performed in an oxygen-free environment.
According to an eleventh aspect of the present invention, in the method of manufacturing a structure for connecting interconnect lines of the tenth aspect, the metallic compound layer includes the metallic clement as a main metallic substance which is a material for the first metal layer.
According to a twelfth aspect of the present invention, in the method of manufacturing a structure for connecting interconnect lines of any one of the ninth to eleventh aspects, the step (b) further comprises the step of (b-3) forming a second metal layer to be in contact with the first copper interconnect line, and the step (b-3), the step (b-2) and the step (b-1) are sequentially performed in this order in an oxygen-free environment.
According to a thirteenth aspect of the present invention, in the method of manufacturing a structure for connecting interconnect lines of the twelfth aspect, the metallic compound layer includes a metallic element as a main metallic substance which is a material for the second metal layer.
According to a fourteenth aspect of the present invention, in the method of manufacturing a structure for connecting interconnect lines of the twelfth or thirteenth aspect, the second metal layer is made of the metallic element having an atomic weight higher than that of copper.
According to a fifteenth aspect of the present invention, the method of manufacturing a structure for connecting interconnect lines of any one of the ninth to fourteenth aspects further comprises the step of: (d) forming a copper film on the first metal layer between the step (b) and the step (c), wherein the second copper interconnect line is formed through electrolytic plating using the copper film as a seed layer, and the step (b-2) and the step (d) are sequentially performed in an oxygen-free environment.
According to the structure for connecting interconnect lines of the first aspect of the present invention, good adhesion between the interposed layer and the second copper interconnect line is obtained. Further, the diffusion of metallic element from the first metal layer into the second copper interconnect line is prevented.
According to the structure for connecting interconnect lines of the second aspect of the present invention, even when there is a large difference in thermal expansion coefficient between the material for the interlayer insulating film and copper, the generation of a void is prevented in the second portion.
According to the structure for connecting interconnect lines of the third aspect of the present invention, the metallic compound layer is operable for reducing interconnection resistance while preventing diffusion of copper from the second copper interconnect line into the outside.
According to the structure for connecting interconnect lines of the fourth aspect of the present invention, the adhesion between the interposed layer and the first copper interconnect line is improved.
According to the structure for connecting interconnect lines of the fifth aspect of the present invention, the increase in interconnection resistance is prevented caused by the diffusion of metallic element into the first copper interconnect line.
According to the structure for connecting interconnect lines of the sixth aspect of the present invention, the interposed layer can be formed within one chamber in one manufacturing device. As a result, cost reduction is realized as compared with the structure including a plurality of chambers required for the layer to be formed of a plurality of metallic elements.
According to the structure for connecting interconnect lines of the seventh and eighth aspects of the present invention, the adhesion between the interposed layer and the second copper interconnect line is improved to a higher degree.
According to the structure for connecting interconnect lines of the ninth aspect of the present invention, the generation of a void in the second copper interconnect line and the diffusion of metallic element from the first metal layer into the second copper interconnect line are prevented.
According to the structure for connecting interconnect lines of the tenth aspect of the present invention, the generation of an oxide film at the interface between the first metal layer and the metallic compound layer is prevented. Therefore, the increase in interface resistance and poor adhesion therebetween are avoided.
According to the structure for connecting interconnect lines of the eleventh aspect of the present invention, the interposed layer can be formed with ease within one chamber in one manufacturing device. As a result, it is easy to sequentially form the metallic compound layer and the first metal layer in an oxygen-free environment.
According to the structure for connecting interconnect lines of the twelfth aspect of the present invention, the adhesion between the interposed layer and the second metal layer is improved. Further, the generation of an oxide film at the interface between the second metal layer and the metallic compound layer is prevented. Therefore, the increase in interface resistance and poor adhesion therebetween are avoided.
According to the structure for connecting interconnect lines of the thirteenth aspect of the present invention, the interposed layer can be formed with ease within one chamber in one manufacturing device. As a result, it is easy to sequentially form the metallic compound layer and the second metal layer in an oxygen-free environment.
According to the structure for connecting interconnect lines of the fourteenth aspect of the present invention, the diffusion of metallic element from the second metal layer into the first copper interconnect line is prevented.
According to the structure for connecting interconnect lines of the fifteenth aspect of the present invention, the generation of an oxide film between the second copper interconnect line and the interposed layer is prevented. Therefore, poor adhesion between the second copper interconnect line and the copper film and the increase in interconnection resistance are avoided.
It is therefore an object of the present invention to provide a technique for connecting interconnect lines for the improvement in reliability of copper interconnect lines.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.